1. Field of the Invention
The present invention is generally related to a marine propulsion system and, more particularly, to a marine propulsion system that is able to control the operating speed of a water pump as a function of one or more measured parameters relating to the internal combustion engine of the marine propulsion system.
2. Description of the Prior Art
Various types of marine propulsion systems are well known to those skilled in the art. These include outboard motors, sterndrive systems which are also referred to as inboard/outboard drives, and inboard systems. When an internal combustion engine is used in combination with a marine propulsion system, some means must be provided to remove heat from the engine. Most marine propulsion systems draw water from the body of water in which the marine vessel is operated and conduct that water through a path which is in thermal communication with the internal combustion engine.
U.S. Pat. No. 4,728,306, which issued to Schneider on Mar. 1, 1988, discloses a marine propulsion auxiliary cooling system. The marine propulsion auxiliary cooling system is provided by an electric auxiliary water pump pumping sea water to cool the engine and/or fuel line after turning off the engine to prevent vaporization of the fuel, or in response to another given engine condition.
U.S. Pat. No. 3,908,579, which issued to Miller et al on Sep. 30, 1875, describes an outboard motor with a dual cooling system. The system defines a first water jacket system adjacent to first and second rotor cavities and having inlet and outlet ports. A housing assembly comprises wall surfaces which define aligned trochoid shaped rotor cavities and additional wall surfaces defining a water jacket system adjacent to other rotor cavities and having inlet and outlet ports. The system also comprises a water pump driven by the engine and having an inlet communicating with the water, and a water conduit communicating between the water pump and the water jacket system inlet ports.
U.S. Pat. No. 4,016,825, which issued to Pichl on Apr. 12, 1977, describes a device for driving a boat propeller and cooling water pump. The device for powering a propeller and a cooling water pump by a boat engine via a downwardly directed drive leg is disclosed in which it supports a hollow intermediate shaft for driving the propeller shaft. Between the crankshaft and the intermediate shaft there is arranged a reversible gear device. A shaft for powering the cooling water pump impeller is rigidly attached to the engine crankshaft and rotatably passes through the intermediate shaft to the impeller.
U.S. Pat. No. 4,592,733, which issued to Bland on Jun. 3, 1986, describes a water pump for a marine propulsion device. The marine propulsion device comprises an engine and a cooling jacket and a fuel pump assembly for circulating water through the cooling jacket. The fluid pump assembly comprises a housing including a pump chamber, an impeller within the housing, a driveshaft extending into the pump, means for rotating the driveshaft, and an interengaging means on the driveshaft and on the impeller for driving the impeller with the driveshaft so as to locate the driveshaft and the impeller in a single driving relation to each other.
U.S. Pat. No. 4,832,639, which issued to Karls et al on May 23, 1989, discloses a marine drive with air trap in auxiliary water inlet. A marine propulsion unit has a depending gearcase with one or more water inlet openings in the sides of the gearcase for supplying water to a water pump, and an auxiliary water inlet opening at an anti-ventilation plate above the propeller for supplying additional water to the water pump. The water passage from the auxiliary water inlet opening to the water pump has a portion extending downwardly below the level of the auxiliary water inlet opening and communicating with the side water inlet openings. When the side water inlet openings are below the water line and the auxiliary water inlet is above the water line, water is received in the downwardly extending portion of the second passage and blocks air from flowing from the auxiliary inlet opening to the water pump, to prevent engine overheating.
U.S. Pat. No. 5,904,605, which issued to Kawasaki et al on May 18, 1999, describes a cooling apparatus for an outboard motor. The apparatus is provided with a water-cooled engine in a vertical alignment in which a crank shaft is vertically disposed, the engine being composed of a cylinder block, a cylinder head and an exhaust manifold into which water jackets are formed respectively and the water jackets are supplied with cooling water from a water pump disposed below the engine in a state mounted to a hull, the cooling apparatus comprising a cylinder cooling-water passage for supplying cooling water from the water pump to the water jackets of the cylinder block and the cylinder head, an exhaust cooling-water passage for supplying cooling water from the water pump to the water jacket of the exhaust manifold, the cylinder cooling-water passage and the exhaust cooling-water passage being independently disposed from each other and being joined together at downstream portions thereof, a thermostat providing for the water jacket of the cylinder block and a sensor for detecting a temperature of the cylinder surface provided for the water jacket of the cylinder block at a portion between the water jacket thereof and the thermostat.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In most known marine propulsion systems, the water pump is driven mechanically and directly by the drive shaft of the system. Therefore, the rotatable portion of the water pump is constantly turning at a rate determined by the speed of the drive shaft. Depending on the particular sizes of the conduits and orifices associated with the cooling system of the engine and depending on the speed of the engine, these known systems often deliver more cooling water to the engine cooling system than is needed under normal conditions. Excess water is commonly conducted to the exhaust system of the engine. If more water is being pumped from the body of water in which the vessel is operating than is needed for removing heat from the engine and its exhaust system, certain components can be cooled to temperatures that are below their optimum levels. Thermostats can be used to regulate the amount of water flowing directly into the engine cooling system, but excess water pumped by the water pump must then be conducted back to the body of water in some manner and along some path. Typically, excess water is conducted into the exhaust system of the engine. As a result, certain regions of the marine propulsion system can be cooled to temperatures below their optimum magnitudes. Furthermore, if more water is being pumped by the water pump than is needed by the internal combustion engine for purposes of removing heat, power is wasted by pumping excess water that is not actually needed or used. It would therefore be significantly beneficial if a water cooling system could be provided for a marine propulsion system which draws only the amount of water from the body of water that is needed to maintain the optimum operation of the internal combustion engine and its exhaust system.
A preferred embodiment of the present invention provides a marine propulsion system which comprises an internal combustion engine having a liquid cooling system and a drive unit of the marine propulsion system which is at least partially submersible in a body of water in which the marine propulsion system is operable. The drive unit is connected in torque transmitting relation with an output shaft of the internal combustion engine.
A water pump, located within the drive unit, has a water inlet and a water outlet. The water inlet is disposable in fluid communication with the body of water in which the marine vessel is operated and the water outlet is disposed in fluid communication with the liquid cooling system of the internal combustion engine. By using this arrangement, the water pump can draw water from the body of water in which a marine vessel is operated and cause that water to be pumped toward and into the cooling system of the internal combustion engine. An electric motor is provided with a rotor connected in torque transmitting relation with the rotatable member of the water pump. The water pump can be a vane pump in which a rotor having a plurality of vanes is rotated within a stator to pump water from the body is of water toward and through the liquid cooling system.
The present further comprises an engine controller connected in signal communication with the electric motor and a first sensor connected in signal communication with the engine controller. The engine controller controls the operating speed of the electric motor as a function of a first parameter sensed by the first sensor. In a typical application of the present invention, the first sensor is a temperature sensor and the first parameter is an engine coolant temperature. The engine coolant temperature can be measured within an internal passage of the engine""s cooling system. If the engine cooling system is a closed system, in which sea water is passed in thermal communication with a coolant contained within a closed system, the temperature of the coolant within the closed system can be used for the purposes of the present invention and can be sent by the first sensor. The engine controller controls the operating speed of the electric motor by transmitting pulse width modulated (PWM) signals to the electric motor in a preferred embodiment of the present invention.
The present invention can further comprise a second sensor connected in signal communication with the engine controller, wherein the engine controller controls the operating speed of the electric motor as a function of both the first parameter sensed by the first sensor and a second parameter sensed by the second sensor. The second sensor can be a tachometer and the second parameter can be engine speed. In certain embodiments, the engine controller can control the speed of the electric motor, and therefore the speed of the pump, as a dual function of both engine speed and coolant temperature. The marine propulsion system can be a sterndrive system and, in a preferred embodiment, the engine controller can comprise a microprocessor.